Crate renaming allows for invalid characters without a warning

[shepmaster]

Problem

[package]
name = "example"
version = "0.1.0"
edition = "2018"

[dependencies]
"haha this isn't a valid name 🐛" = { package = "libc", version = "0.1" }

$ cargo build --verbose
       Fresh libc v0.1.12
   Compiling xz v0.1.0 (/private/tmp/xz)
     Running `rustc --edition=2018 --crate-name xz src/main.rs --color always --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=7ea0f6c7f3b6b365 -C extra-filename=-7ea0f6c7f3b6b365 --out-dir /private/tmp/xz/target/debug/deps -C incremental=/private/tmp/xz/target/debug/incremental -L dependency=/private/tmp/xz/target/debug/deps --extern 'haha this isn'\''t a valid name 🐛=/private/tmp/xz/target/debug/deps/liblibc-aee2768e37366de4.rlib'`

Possible Solution(s)

I'd expect a warning when the key names are not valid Rust identifiers.

Notes

$ cargo --version --verbose
cargo 1.32.0 (8610973aa 2019-01-02)
release: 1.32.0
commit-hash: 8610973aaf48615ba7dc9a38a9a2795ba6f36a31
commit-date: 2019-01-02

[alexcrichton]

Oh dear, that's definitely a bug!

[lukaslueg]

Is it too heavy handed to add a call to valid_package_name() here? We actually allow dependencies named "!", only failing to resolve.

[ehuss]

I would probably validate during toml parsing (somewhere like here).

[mbStavola]

I'd like to take this!